1. Field of the Invention
The present invention relates to apparatuses for controlling, using a pair of a crank signal and a cam signal, an engine installed in, for example, a vehicle.
2. Description of the Related Art
Engine control units for vehicles use a crank signal whose signal level varies in a predetermined same direction at regular rotation angles (regular crank angles) of an engine crankshaft. Specifically, the crank signal is measured by a crankshaft sensor connected to an engine control unit, and the measured crank signal is input, through an input path, to the engine control unit operating in a main control mode.
Specifically, the engine control unit works to identify a rotational position (crank position) of the crankshaft based on the crank signal in the main control mode.
Each time it is determined that the identified rotational position of the crankshaft is matched with a desired rotational position, the engine control unit works to generate events associated with engine control, such as fuel injection or ignition in the main control mode.
In such an engine control unit using the crank signal for engine control, if the crank signal cannot be input normally to the engine control unit due to, for example, a break in wires connecting the crankshaft sensor and the engine control unit, the engine control unit cannot identify the rotational position of the crankshaft. This may cause the engine control unit not to continuously carry out proper control of the engine.
In order to address the problem, when the crank signal cannot be input normally to the engine control unit, the engine control unit is configured to operate in a sub control mode using a can signal measured by a cam sensor and inputted thereto through the input path. The cam signal has a level that varies in a predetermined same direction at regular rotation angles of an engine camshaft.
This allows the engine control unit to continuously generate events associated with engine control based on the cam signal during the sub control mode.
Specifically, when an occurrence of a failure in the crank signal is detected, the engine control unit is configured to switch its operation mode from the main control mode using the crank signal to the sub control mode using the cam signal so as to continuously carry out engine control. The engine control of the engine control unit in the sub control mode allows the vehicle to be driven in a limp-home mode, such as driven to a safe place slowly. Such an engine control unit is disclosed in US Patent Application Publication No. 20070175272 corresponding to Japanese Patent Application Publication No. 2007-205242.
Such an engine control unit monitors the variation pattern of the level of the crank signal inputted through the input path, and determines that the crank signal is abnormally inputted thereto when:
the variation pattern of the level of the crank signal is different from a proper variation pattern of the level of the crank signal, and
the level of the difference exceeds an allowable level.
After the abnormality detection and the switching from the crank signal to the cam signal, the engine control unit cannot properly detect that a failure occurs in the crank signal. This is because the variation pattern of the cam signal is different from that of the crank signal.
Note that, after a failure has occurred in the crank signal, the engine control unit needs to drive the vehicle in the limp-home mode. Therefore, after the occurrence of an abnormality in the crank signal, the engine control unit is normally configured to switch a signal to be inputted through the input path from the crank signal to the cam signal, and simultaneously stop monitoring a signal inputted through the input path.
However, after a short-term abnormality has occurred in the crank signal, when the crank signal can get back to normal, the engine control unit cannot monitor the variation pattern of the level of the crank signal because the cam signal is inputted through the input path to the engine control unit. Thus, it is desired for the engine control unit to monitor whether an abnormality, occurs in the crank signal after the cam signal has been switched to be inputted to the engine control unit through the input path from the crank signal.
This is because, if the crank signal got back to a normal so that a signal to be inputted to the engine control unit were switched again from the cam signal to the crank signal, it would be possible for the engine control unit to return its operation mode from the sub control mode to the main control mode.